Add an assertion

diff --git a/source/base/incremental_function.cc b/source/base/incremental_function.cc
index d65d479e9e7565f2b9994f0cccd95bd619eafdca..027424e6d9ccdc3d5426ca671de57d0458d15177 100644 (file)
--- a/source/base/incremental_function.cc
+++ b/source/base/incremental_function.cc
@@ -36,6 +36,8 @@ namespace Functions
   IncrementalFunction<dim, RangeNumberType>::set_decrement(
     const time_type delta)
   {
+    Assert(delta >= 0.0,
+           ExcMessage("The decrement must be set to a non-negative value."));
     delta_t = delta;
   }